More Letters of Charles Darwin — Volume 2

One word to thank you. I declare, had it not been for your kindness, we should have broken down. As it is we have made out clearly that with some plants (chiefly succulent) the bloom checks evaporation — with some certainly prevents attacks of insects; with SOME sea-shore plants prevents injury from salt water, and, I believe, with a few prevents injury from pure water resting on the leaves. This latter is as yet the most doubtful and the most interesting point in relation to the movements of plants.

(736/5. Modern research, especially that of Stahl on transpiration ("Bot. Zeitung," 1897, page 71) has shown that the question is more complex than it appeared in 1877. Stahl's point of view is that moisture remaining on a leaf checks the transpiration-current; and by thus diminishing the flow of mineral nutriment interferes with the process of assimilation. Stahl's idea is doubtless applicable to the whole problem of bloom on leaves. For other references to bloom see letters 685, 689 and 693.)

LETTER 737. TO J.D. HOOKER. Down, August 19th, 1873.

The next time you walk round the garden ask Mr. Smith (737/1. Probably John Smith (1798-1888), for some years Curator, Royal Gardens, Kew.), or any of your best men, what they think about injury from watering during sunshine. One of your men — viz., Mr. Payne, at Abinger, who seems very acute — declares that you may water safely any plant out of doors in sunshine, and that you may do the same for plants under glass if the sashes are opened. This seems to me very odd, but he seems positive on the point, and acts on it in raising splendid grapes. Another good gardener maintains that it is only COLD water dripping often on the same point of a leaf that ever injures it. I am utterly perplexed, but interested on the point. Give me what you learn when you come to Down.

I should like to hear what plants are believed to be most injured by being watered in sunshine, so that I might get such.

I expect that I shall be utterly beaten, as on so many other points; but I intend to make a few experiments and observations. I have already convinced myself that drops of water do NOT act as burning lenses.

LETTER 738. TO J.D. HOOKER. December 20th {1873}.

I find that it is no use going on with my experiments on the evil effects of water on bloom-divested leaves. Either I erred in the early autumn or summer in some incomprehensible manner, or, as I suspect to be the case, water is only injurious to leaves when there is a good supply of actinic rays. I cannot believe that I am all in the wrong about the movements of the leaves to shoot off water.

The upshot of all this is that I want to keep all the plants from Kew until the spring or early summer, as it is mere waste of time going on at present.

LETTER 739. TO W. THISELTON-DYER. Down, July 22nd {1877}.

Many thanks for seeds of the Malva and information about Averrhoa, which I perceived was sensitive, as A. carambola is said to be; and about Mimosa sensitiva. The log-wood {Haematoxylon} has interested me much. The wax is very easily removed, especially from the older leaves, and I found after squirting on the leaves with water at 95 deg, all the older leaves became coated, after forty-eight hours, in an astonishing manner with a black Uredo, so that they looked as if sprinkled with soot and water. But not one of the younger leaves was affected. This has set me to work to see whether the "bloom" is not a protection against parasites. As soon as I have ascertained a little more about the case (and generally I am quite wrong at first) I will ask whether I could have a very small plant, which should never be syringed with water above 60 deg, and then I suspect the leaves would not be spotted, as were the older ones on the plant, when it arrived from Kew, but nothing like what they were after my squirting.

In an old note of yours (which I have just found) you say that you have a sensitive Schrankia: could this be lent me?

I have had lent me a young Coral-tree (Erythrina), which is very sickly, yet shows odd sleep movements. I suppose I could buy one, but Hooker told me first to ask you for anything.

Lastly, have you any seaside plants with bloom? I find that drops of sea-water corrode sea-kale if bloom is removed; also the var. littorum of Triticum repens. (By the way, my plants of the latter, grown in pots here, are now throwing up long flexible green blades, and it is very odd to see, ON THE SAME CULM, the rigid grey bloom-covered blades and the green flexible ones.) Cabbages, ill-luck to them, do not seem to be hurt by salt water. Hooker formerly told me that Salsola kali, a var. of Salicornia, one species of Suaeda, Euphorbia peplis, Lathyrus maritimus, Eryngium maritimum, were all glaucous and seaside plants. It is very improbable that you have any of these or of foreigners with the same attributes.

God forgive me: I hope that I have not bored you greatly.

By all the rules of right the leaves of the logwood ought to move (as if partially going to sleep) when syringed with tepid water. The leaves of my little plant do not move at all, and it occurs to me as possible, though very improbable, that it would be different with a larger plant with perhaps larger leaves. Would you some day get a gardener to syringe violently, with water kept in a hothouse, a branch on one of your largest logwood plants and observe {whether?} leaves move together towards the apex of leaf?

By the way, what astonishing nonsense Mr. Andrew Murray has been writing about leaves and carbonic acid! I like to see a man behaving consistently...

What a lot I have scribbled to you!

(FIGURE 13. Leaf of Trifolium resupinatum (from a drawing by Miss Pertz).)

LETTER 740. TO W. THISELTON-DYER. {August, 1877.}

There is no end to my requests. Can you spare me a good plant (or even two) of Oxalis sensitiva? The one which I have (formerly from Kew) has been so maltreated that I dare not trust my results any longer.

Please give the enclosed to Mr. Lynch. (740/1. Mr. Lynch, now Curator of the Cambridge Botanic Garden, was at this time in the R. Bot. Garden, Kew. Mr. Lynch described the movements of Averrhoa bilimbi in the "Linn. Soc. Journ," Volume XVI., page 231. See also "The Power of Movement in Plants," page 330.) The spontaneous movements of the Averrhoa are very curious.

You sent me seeds of Trifolium resupinatum, and I have raised plants, and some former observations which I did not dare to trust have proved accurate. It is a very little fact, but curious. The half of the lateral leaflets (marked by a cross) on the lower side have no bloom and are wetted, whereas the other half has bloom and is not wetted, so that the two sides look different to the naked eye. The cells of the eipdermis appear of a different shape and size on the two sides of the leaf {Figure 13}.

When we have drawings and measurements of cells made, and are sure of our facts, I shall ask you whether you know of any case of the same leaf differing histologically on the two sides, for Hooker always says you are a wonderful man for knowing what has been made out.

(740/2. The biological meaning of the curious structure of the leaves of Trifolium resupinatum remains a riddle. The stomata and (speaking from memory) the trichomes differ on the two halves of the lateral leaflets.)

LETTER 741. TO L. ERRERA.

(741/1. Professor L. Errera, of Brussels wrote, as a student, to Darwin, asking permission to send the MS. of an essay by his friend S. Gevaert and himself on cross and self-fertilisation, and which was afterwards published in the "Bull. Soc. Bot. Belg." XVII., 1878. The terms xenogamy, geitonogamy, and autogamy were first suggested by Kerner in 1876; their definition will be found at page 9 of Ogle's translation of Kerner's "Flowers and their Unbidden Guests," 1878. In xenogamy the pollen comes from another PLANT; in geitonogamy from another FLOWER on the same PLANT; in autogamy from the androecium of the fertilised FLOWER. Allogamy embraces xenogamy and geitonogamy.)

Down, October 4th, 1877.

I have now read your MS. The whole has interested me greatly, and is very clearly written. I wish that I had used some such terms as autogamy, xenogamy, etc...I entirely agree with you on the a priori probability of geitonogamy being more advantageous than autogamy; and I cannot remember having ever expressed a belief that autogamy, as a general rule, was better than geitonogamy; but the cases recorded by me seem too strong not to make me suspect that there was some unknown advantage in autogamy. In one place I insert the caution "if this be really the case," which you quote. (741/2. See "Cross and Self-Fertilisation," pages 352, 386. The phrase referred to occurs in both passages; that on page 386 is as follows: "We have also seen reason to suspect that self-fertilisation is in some peculiar manner beneficial to certain plants; but if this be really the case, the benefit thus derived is far more than counterbalanced by a cross with a fresh stock or with a slightly different variety." Errera and Gevaert conclude (pages 79-80) that the balance of the available evidence is in favour of the belief that geitonogamy is intermediate, in effectiveness, between autogamy and xenogamy.) I shall be very glad to be proved to be altogether in error on this point.

Accept my thanks for pointing out the bad erratum at page 301. I hope that you will experimentise on inconspicuous flowers (741/3. See Miss Bateson, "Annals of Botany," 1888, page 255, "On the Cross-Fertilisation of Inconspicuous Flowers: " Miss Bateson showed that Senecio vulgaris clearly profits by cross-fertilisation; Stellaria media and Capsella bursa-pastoris less certainly.); if I were not too old and too much occupied I would do so myself.

Finally let me thank you for the kind manner in which you refer to my work, and with cordial good wishes for your success...

LETTER 742. TO W. THISELTON-DYER. Down, October 9th, 1877.

One line to thank you much about Mertensia. The former plant has begun to make new leaves, to my great surprise, so that I shall be now well supplied. We have worked so well with the Averrhoa that unless the second species arrives in a very good state it would be superfluous to send it. I am heartily glad that you and Mrs. Dyer are going to have a holiday. I will look at you as a dead man for the next month, and nothing shall tempt me to trouble you. But before you enter your grave aid me if you can. I want seeds of three or four plants (not Leguminosae or Cruciferae) which produce large cotyledons. I know not in the least what plants have large cotyledons. Why I want to know is as follows: The cotyledons of Cassia go to sleep, and are sensitive to a touch; but what has surprised me much is that they are in constant movement up and down. So it is with the cotyledons of the cabbage, and therefore I am very curious to ascertain how far this is general.

LETTER 743. TO W. THISELTON-DYER. Down, October 11th {1877}.

The fine lot of seeds arrived yesterday, and are all sown, and will be most useful. If you remember, pray thank Mr. Lynch for his aid. I had not thought of beech or sycamore, but they are now sown.

Perhaps you may like to see a rough copy of the tracing of movements of one of the cotyledons of red cabbage, and you can throw it into the fire. A line joining the two cotyledons stood facing a north-east window, and the day was uniformly cloudy. A bristle was gummed to one cotyledon, and beyond it a triangular bit of card was fixed, and in front a vertical glass. A dot was made in the glass every quarter or half hour at the point where the end of the bristle and the apex of card coincided, and the dots were joined by straight lines. The observations were from 10 a.m. to 8.45 p.m. During this time the enclosed figure was described; but between 4 p.m. and 5.38 p.m. the cotyledon moved so that the prolonged line was beyond the limits of the glass, and the course is here shown by an imaginary dotted line. The cotyledon of Primula sinensis moved in closely analogous manner, as do those of a Cassia. Hence I expect to find such movements very general with cotyledons, and I am inclined to look at them as the foundation for all the other adaptive movements of leaves. They certainly are of the so-called sleep of plants.

I hope I have not bothered you. Do not answer. I am all on fire at the work.

I have had a short and very prosperous note from Asa Gray, who says Hooker is very prosperous, and both are tremendously hard at work. (743/1. "Hooker is coming over, and we are going in summer to the Rocky Mountains together, according to an old promise of mine." Asa Gray to G.F. Wright, May 24th, 1877 ("Letters of Asa Gray," II., page 666).)

LETTER 744. TO H. MULLER. Down, January 1st {1878?}.

I must write two or three lines to thank you cordially for your very handsome and very interesting review of my last book in "Kosmos," which I have this minute finished. (744/1. "Forms of Flowers," 1877. H. Muller's article is in "Kosmos," II., page 286.) It is wonderful how you have picked out everything important in it. I am especially glad that you have called attention to the parallelism between illegitimate offspring of heterostyled plants and hybrids. Your previous article in "Kosmos" seemed to me very important, but for some unknown reason the german was very difficult, and I was sadly overworked at the time, so that I could not understand a good deal of it. (744/2. "Kosmos," II., pages 11, 128. See "Forms of Flowers," Edition II., page 308.) But I have put it on one side, and when I have to prepare a new edition of my book I must make it out. It seems that you attribute such cases as that of the dioecious Rhamnus and your own of Valeriana to the existence of two forms with larger and smaller flowers. I cannot follow the steps by which such plants have been rendered dioecious, but when I read your article with more care I hope I shall understand. (744/3. See "Forms of Flowers," Edition II., pages 9 and 304. H. Muller's view is briefly that conspicuous and less conspicuous varieties occurred, and that the former were habitually visited first by insects; thus the less conspicuous form would play the part of females and their pollen would tend to become superfluous. See H. Muller in "Kosmos," II.) If you have succeeded in explaining this class of cases I shall heartily rejoice, for they utterly perplexed me, and I could not conjecture what their meaning was. It is a grievous evil to have no faculty for new languages.

With the most sincere respect and hearty good wishes to you and all your family for the new year...

P.S. — What interesting papers your wonderful brother has lately been writing!

LETTER 745. TO W. THISELTON-DYER.

(745/1. This letter refers to the purchase of instruments for the Jodrell Laboratory in the Royal Gardens, Kew. "The Royal Commission on Scientific Instruction and the Advancement of Science, commonly spoken of as the Devonshire Commission, in its fourth Report (1874), page 10, expressed the opinion that 'it is highly desirable that opportunities for the pursuit of investigations in Physiological Botany should be afforded at Kew to those persons who may be inclined to follow that branch of science.' Effect was given to this recommendation by the liberality of the late T.J. Phillips-Jodrell, M.A., who built and equipped the small laboratory, which has since borne his name, at his own expense. It was completed and immediately brought into use in 1876." The above is taken from the "Bulletin of Miscellaneous Information," R. Botanic Gardens, Kew, 1901, page 102, which also gives a list of work carried out in the laboratory between 1876 and 1900.)

Down, March 14th, 1878.

I have a very strong opinion that it would be the greatest possible pity if the Phys{iological} Lab., now that it has been built, were not supplied with as many good instruments as your funds can possibly afford. It is quite possible that some of them may become antiquated before they are much or even at all used. But this does not seem to me any argument at all against getting them, for the Laboratory cannot be used until well provided; and the mere fact of the instruments being ready may suggest to some one to use them. You at Kew, as guardians and promoters of botanical science, will then have done all in your power, and if your Lab. is not used the disgrace will lie at the feet of the public. But until bitter experience proves the contrary I will never believe that we are so backward. I should think the German laboratories would be very good guides as to what to get; but Timiriazeff of Moscow, who travelled over Europe to see all Bot. Labs., and who seemed so good a fellow, would, I should think, give the best list of the most indispensable instruments. Lately I thought of getting Frank or Horace to go to Cambridge for the use of the heliostat there; but our observations turned out of less importance than I thought, yet if there had been one at Kew we should probably have used it, and might have found out something curious. It is impossible for me to predict whether or not we should ever want this or that instrument, for we are guided in our work by what turns up. Thus I am now observing something about geotropism, and I had no idea a few weeks ago that this would have been necessary. In a short time we might earnestly wish for a centrifugal apparatus or a heliostat. In all such cases it would make a great difference if a man knew that he could use a particular instrument without great loss of time. I have now given my opinion, which is very decided, whether right or wrong, and Frank quite agrees with me. You can, of course, show this letter to Hooker.

LETTER 746. TO F. LUDWIG. Down, May 29th, 1878.

I thank you sincerely for the trouble which you have taken in sending me so long and interesting a letter, together with the specimens. Gradations are always very valuable, and you have been remarkably successful in discovering the stages by which the Plantago has become gyno-dioecious. (746/1. See F. Ludwig, "Zeitsch. f. d. Geo. Naturwiss." Bd. LII., 1879. Professor Ludwig's observations are quoted in the preface to "Forms of Flowers," Edition II., page ix.) Your view of its origin, from being proterogynous, seems to me very probable, especially as the females are generally the later-flowering plants. If you can prove the reverse case with Thymus your view will manifestly be rendered still more probable. I have never felt satisfied with H. Muller's view, though he is so careful and admirable an observer. (746/2. See "Forms of Flowers," Edition II., page 308. Also letter 744.) It is more than seventeen years since I attended to Plantago, and when nothing had been published on the subject, and in consequence I omitted to attend to several points; and now, after so long an interval, I cannot pretend to say to which of your forms the English one belongs; I well remember that the anther of the females contained a good deal {of} pollen, though not one sound grain.

P.S. — Delpino is Professor of Botany in Genoa, Italy (746/3. Now at Naples.); I have always found him a most obliging correspondent.

LETTER 747. TO W. THISELTON-DYER. Down, August 24th {1878}.